The present invention relates to a machine tool with mobile crossbeams, mobile uprights or mobile gantry structure.
The invention relates in particular to a device for driving the crossbeams in a machine tool mounted on a frame and where the crossbeams have machining units mounted on them.
In certain mechanical engineering industries, such as the automotive and aeronautical industries, where components to be machined may be extremely large, the automatic machinery used must be designed to support large bulky workpieces. For this reason, automatic machine tools or machining centers are known to have two parallel longitudinal guides each supported by a corresponding upright. The operating units that machine the workpiece are mounted on crossbeams which run in the guides.
In known machines of this type, the sliding crossbeams running in the longitudinal guides are driven by mechanical actuating devices which position each crossbeam at the position necessary to machine the workpiece and which move the crossbeam itself so as to start the feed motion of the machining unit.
Mechanical devices for driving the sliding crossbeams, such as, for example, devices with rack and pinion mechanisms or recirculating ball screws, have several drawbacks. One of the drawbacks is the relative slowness with which the crossbeams are moved along the guides. This slowness leads to extremely lengthy starting response times and limited acceleration rates depending also on the bulk and weight of the mechanical parts concerned.
Another drawback connected with the use of these mechanical driving devices is that the frictional forces applied to the guides, again depending on the bulk and weight of the sliding crossbeams, are proportionally very high. This leads to rapid overheating and wear of the mechanical components.
Other drawbacks of conventional mechanical driving devices are due to the frequent adjustments they require in order to reduce the measurement errors that occur also on account of the considerable lengths traveled by the crossbeams in the longitudinal guides.
The present invention has for an object to provide a machine tool with mobile crossbeams that overcomes the above mentioned drawbacks.
Accordingly, the invention provides a machine tool comprising two parallel longitudinal guides extending in a first principal direction, two substantially parallel crossbeams extending in a second direction substantially perpendicular to the first principal direction of the longitudinal guides, the crossbeams mounting respective machining units and running in the guides in the first direction. In the machine according to the invention, the drive motion for the sliding crossbeams running in the guides is provided by linear electric motors.